I might as well weigh in on St. Melissa...
First of all, Melissa Etheridge is an iconic figure and she is truly incredible.
Second, theatre has an amazing ability to allow various interpretations of things, and this is a perfect example.
But the main point I want to make is this:
St. Jimmy (to me) is a manifestation of Johnny's self-destructive alter-ego. Johnny, like all of us, has many inner demons, and they may present themselves at various times in different forms. They may be male, female, young, old, attractive, ugly, or any number of other manifestations. I think that a variety of St. Jimmys is actually the perfect way to go. It shows the instability of St. Jimmy, that any one of Johnny's demons can take control and then self destruct.